Yutyrannus: The Fuzzy Dinosaur

Yutyrannus Had Primitive Feathers

Image Credit: Brian Choo

Isn’t science awesome? Palaeontologists announced that a giant, feather-covered dinosaur (a type of tyrannosaur) has recently been discovered and described. It was named Yutyrannus huali by the authors of the description, Xu Xing et al. Three well-preserved skeletons were found of the carnivorous species that reached nearly 30 feet in adult form; it lived about 125 million years ago. The remarkable feature of this find is that the body was clad in wispy, fine feathers unlike those of modern birds; the simple feather structure is rather described as ‘dino-fuzz’. Yutyrannus is thus far the biggest animal with plumage that has ever been found.

Yutyrannus is Not the First Dinosaur with Fuzz

This amazing discovery is not entirely unexpected, since it confirms a previously-stated hypothesis from eight years ago. In 2004 another discovery of a smaller tyrant (named Dilong paradoxus) was made by Xu and co-workers. It was a small coelurosaur that lived ca. five million years earlier than Yutyrannus, and it was also covered with simple fuzz. Dilong was most likely an ancient tyrannosauroid, situated basally within the family that produced later tyrants (e.g. Teratophoneus and Gorgosaurus). If Dilong, and hence tyrannosauroids, sported feathers, then most lineages that are closely related to it are also likely to have had feathers. This means that even Tyrannosaurus rex could have had a partial coating of feathers.

Young Tyrannosaurs May Have Been Fluffy Like Yutyrannus

The idea that giant tyrannosaurs may have had feathers has been considered before, but evidence was lacking. North American fossils of tyrannosaurs did not form in the type of environments that were conducive to the accurate preservation of feathers. Although never published, there have been rumours that adult tyrannosaur skin samples pointed towards them having naked hides. It is possible that young tyrannosaurs (chicks) were fluffy with dino-fuzz, but that feathers were lost in adult forms once insulation was no longer needed.

It’s Hard For Many to Believe Dinosaurs May Have Had Feathers

The idea of feathered tyrannosaurs has not been welcomed in all quarters. On the humor site Cracked.com a drawing of a feathered Tyrannosaurus is included as one of ’17 Images That Will Ruin Your Childhood’, while strong negative response was received when the same image was posted on BuzzFeed. Most people tend to cling to the smooth-skinned image of tyrannosaurs, popularised by movies such as ‘Jurassic Park’. There are, however, some supporters of the idea that large tyrannosaurs could have been at least partially feathered with dino-fuzz. While this could change the image of drab-looking, scaly dinosaurs, there is no doubt that they would still demand respect.

No One Is Sure How Fuzzy Yutyrannus Was

It is not certain how much of the Yutyrannus body was clad with dino-fuzz. The drawings by Brian Choo are great, and it is fair to assume a full covering of fuzz, but the three fossils only had feather patches in a few spots – on the neck, arm, foot, hip and tail. Despite the temptation to assume full coverage from this evidence, it is always possible that non-avian dinosaurs had feathers restricted to certain areas only.

Feathers Can Indicate a Dinosaur’s Color

The feather discovery may shed light on what color Yutyrannus was. The color schemes of small feathered dinosaurs (e.g. Microraptor, Archaeopteryx, Anchiornis) have been determined from feathers, so it should be possible in this case too. Will Yutyrannus turn out to be dark like previously studied species, or did it have a different hue? Time will tell, since the research is already being carried out by Xu and co-workers.

Yutyrannus May Not Be a Tyrannosaur

There are two potential twists in this tale. Firstly, it is possible that Yutyrannus may not be a tyrannosaur. According to palaeontologist Darren Naish, this species shares slight similarities with the carcharodontosaurids, which is a sub-group of larger predators with close relations to Allosaurus. Future studies will have to confirm to which exact lineage Yutyrannus belongs.

If it is confirmed that the predatory Yutyrannus is not a tyrannosauroid after all, then it would become even more important. Initial research showed that only the coelurosaurs (which includes tyrannosauroids and a few other theropod clades, such as birds) possessed feathers. Subsequent discoveries then revealed the presence of feather-like structures on two dinosaurs that are far removed in terms of lineage. These are Psittacosaurus (a small ceratopsian dinosaur) and Tianyulong (a tiny, bipedal, herbivorous dinosaur).

Feathers Can Tell A Lot About Dinosaur Lineage

The distribution of feather-like structures across dinosaur lineages may suggest that these secondary body coverings have evolved more than once on different parts of the family tree. It may also suggest that this is a basal character state that has been lost in some dinosaur clades, but retained in others. This is where the placing of Yutyrannus on the family tree becomes important: if new evidence shows that is does not belong in the coelurosaur clade, but rather with carcharodontosaurids or elsewhere, then it forms another unique placement of feathers on the family tree, which means that an even broader range of species had feathers.

Juravenator Also Had Dino-Fuzz

Another find of an earlier and smaller theropod (called Juravenator) also showed traces of dino-fuzz. Like Yutyrannus, it may also not be a coelurosaur, which means that a few lineages of dinosaurs (with distant relations to birds) show the presence of feather-like coverings. Yutyrannus may support this view in future, but for now it is assumed to be an ancient form of tyrant dinosaur.

Yutyrannus May Have Been Pack Hunters

The second possible twist is that Yutyrannus may have been hunters that move in well-coordinated packs. This is suggested by the fact that all three fossils, representing individuals of varying sizes, were found together. Previously the discovery of many tyrannosaurs in one bone bed has been used to make this conclusion. Xu suggests that the presence of a sauropod skeleton also shows that the three Yutyrannus were part of a pack that attacked the larger sauropod, and all four happened to die at the same time.

There is some skepticism about this theory, especially since bone beds can be misleading. Multiple skeletons may occur together since storms or floods forced them there, dead bodies from elsewhere may have washed to the same point, or they could all have been drawn to a predator trap. It is dangerous to make conclusions based on circumstantial evidence without carefully analyzing the geology and taphonomy of such sites.

Whether they hunted alone or in packs, all would agree that Yutyrannus would have been a fantastic sight to behold. Without previous studies that hinted at the possibility that such a feathered / fuzzy hyper-carnivore of a dinosaur could exit, no-one would have imagined it. This type of discovery reminds us again how truly awe inspiring creatures like Yutyrannus were.